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I think, this is Sargent cherry, blooming in wild area along 20 Ave near 144Str.
[Edited by wcutler: it's not clear if this is meant to be Sargent cherry (o-yama-zakura) or Sargent Hybrid cherry; it seems late for either one of them. Maybe it's a seedling of a Sargent Hybrid cherry.]

Not 'Ichiyo'. I thought you were asking 'Shogetsu' or 'Shirofugen'! It's 'Shogetsu', dark pink buds, fine cuts in the petal edges. Larger flowers than 'Ichiyo'. 'Ichiyo' fade to white, but they look faded. These are fresh white. Also, new not even opened leaves here are very green.